Technical Support for
HVAC Contractors

Some warmth during operation is normal. The motor drives the blade against spring tension and holds that position while energized. If the motor is too hot to touch after extended operation, check that the damper blade is not obstructed and that the 24 Vac supply is within specification. If a broken rotor spring is suspected, it can be removed with long-nose pliers — the damper will continue to operate normally without it. If the motor gears are worn or stiff from a long period without use (e.g. summer months), replace the motor. Contact the factory at 1-800-661-7382 for motor replacement details.

This is almost always a wiring issue — the ventilation control output is connected to the wrong terminal on the furnace or air handler, triggering the cooling circuit instead of the fan-only or fresh air circuit. Check that the control wire is connected to the correct terminal as specified in your ADP relay adaptor installation instructions. If you are unsure which terminal is correct for your appliance, call technical support with the furnace model number available.

Start with the signal: if an inline fuse is installed between the stat wire and the damper's black wire #1, check it first. With the control body cover removed, use a jumper across terminals 1 and 5 — if the damper opens, a faulty thermostat is suspected. If the damper does not open, check for mechanical causes: a blade stuck from residue (especially after summer months) can be cleaned with soap and water. Also check for a broken spring in the motor rotor, which can be removed with long-nose pliers without affecting operation, and for worn motor gears — if gears are the cause, replace the motor. Call 1-800-661-7382 for step-by-step guidance.

First confirm the Test/Run switch (if fitted) is in the UP or RUN position. Check that 24 Vac is present at the damper motor terminals. To isolate a faulty motor from a faulty relay: remove the control body cover and use a jumper across terminals 3 and 4. If the damper closes, a faulty relay is indicated — replace the relay kit (SF1 for single-furnace applications, SF2 for two-furnace applications). If the damper does not close when terminals 3 and 4 are jumped, check power supply to terminals 3 and 5, then connect power directly to terminals 4 and 5 — no response indicates a faulty motor. Contact the factory for motor or relay replacement details.

HRV and ERV integration failures most commonly come from control signal mismatch — the HRV/ERV output voltage or signal type may not match the damper input requirements. Confirm the HRV/ERV output is 24 Vac and is wired to the correct terminal on the ADP relay adaptor or directly to the damper motor. If the HRV/ERV uses a dry contact output, the wiring sequence will be different. Contact technical support with the HRV/ERV model number and damper part number.

Cold drafts through a closed damper typically indicate one of three things: the blade is not fully closing due to obstruction or ice load; the action code is wrong for the application (a Power Open damper where Power Close is required); or there is a passive hood elsewhere in the duct run that is always open and bypassing the closed damper. Verify the damper action matches the application, confirm the blade reaches fully closed position, and check there is no passive hood in the same duct run.

The HOM mounts vertically at the appliance end of the combustion air duct — not at the wall penetration. The installation instructions specify mounting the bracket to the side of the appliance or plenum, in the vertical position, with the bottom of the bracket within one foot above the burner level and within two feet horizontally from the front of the appliance. The exterior end of the duct terminates with a passive OOH hood at the building wall.

The HOM must be accessible for wiring. It is recommended (but not required) to orient the damper so air discharges toward the front of the appliance.

For standard 24 Vac furnace applications, the HOM end switch (SF1 for one appliance, SF2 for two appliances) wires directly in series with the thermostat wire to the 'W' terminal of the appliance — the appliance cannot fire until the damper opens and the end switch closes. No ADP relay adaptor is required for 24 Vac circuits. ADP relay adaptors are needed only when connecting to non-24 Vac circuits: use ADP-0MV2-S5A for millivolt (DC) safety control systems and ADP-1102-S5A for 120 Vac systems. Download the full wiring diagram from the Technical Library or call 1-800-661-7382.

Yes — the action can be changed in the field using the following procedure: (1) Remove the motor. (2) Remove the Spring Plate and reverse the direction of the screws in the spring plate, then remount the spring plate inside-out to the other side of the damper — note the proper spring position. (3) Before replacing the motor, check for smooth spring operation. (4) Remount the motor and check for smooth operation of both motor and damper. (5) Update the I.D. and date on the damper to reflect the new action (PO or PC). Note: Round and Adjustable Spring Plates are interchangeable. If an adjustment feature is required after the plate change, contact the factory. Confirming the correct action for the application before installation is still strongly recommended — especially on combustion air applications where the wrong action creates a safety risk.

The Hoyme Timer Adaptor uses a Grasslin interval timer. White pins on the periphery of the timer face can be pulled outward — each pin extended represents 15 minutes of ventilation time. Pull out as many pins as needed to set the desired cycle duration. In addition to the peripheral pins, there is a 3-way manual override pin in the centre of the timer face: the normal operating position is in the middle; moving it to the up 'I' position acts as if all white pins are extended (timer runs continuously); moving it to the down '0' position acts as if no pins are extended (timer is off). If you do not have the timer instructions, they are available in the Technical Library or by calling 1-800-661-7382.

Match the damper diameter to the duct diameter at the installation point — not the appliance inlet collar, and not a transition fitting. For fresh air and combustion air applications, duct size is typically determined by the appliance manufacturer's installation instructions based on BTU input and duct run length. For HRV/ERV fresh air ports, match the HRV/ERV fresh air connection diameter. If the duct transitions size near the installation point, install the damper in the consistent-diameter section of the run.

Hoyme part numbers follow a consistent structure across product families. On the HAC: the first segment is the product family (HAC), the second is the size in two-digit inches (06 = 6"), the third is the relay position (10 = no relay, 11 = relay included), and the fourth is the action/end switch code (OPO = no end switch, power open; SPO = end switch included, power open). The same logic applies to MOH, MAC, and other motorized products. Part number decoders are included on each product page, or call technical support if you need to decode a part number from an existing installation.

If the damper opened but the furnace will not fire, the end switch or its linkage is the first suspect. The end switch is designed to click closed as the blade opens to approximately 30 degrees — confirm this by listening for a click during the opening cycle. If no click is heard, check the end switch lever arm and bend it to suit if the linkage is off. If the click is present but the furnace still does not fire, a faulty end switch is suspected. To bypass the interlock for testing, use the TEST/RUN switch in the down 'TEST' position — if the appliance then fires, the end switch or its circuit is confirmed faulty. If the appliance still does not fire in TEST mode, a fault in the heating appliance system itself is suspected. Call 1-800-661-7382 for further assistance.

Hoyme dampers carry a 2-year electrical warranty and a 10-year mechanical warranty. In practice, the mechanical components — blade, bearings, spring mechanism, and housing — typically last the life of the building. The motor assembly is the serviceable component: replacement motor kits are available from the factory and can be installed in place without replacing the full damper. A motor failure does not mean the damper needs to be replaced.